The invention relates to a drive motor for surgical apparatus, for example, for dental tool holders, for bone drills or bone cutters.
In surgical apparatus of this type, it is necessary to drive the tools at high rotational speeds and, insofar as possible, the drive means should be operable by the energy sources available in a hospital, for example, compressed air.
In known surgical apparatus for example, turbine motors or rotary piston motors driven by compressed air are employed, these having the disadvantage however that they are relatively prone to wear and have to be intensively maintained by means of painstaking lubrication for example.
The object of the invention is to propose a suitable drive motor for use especially with surgical apparatus, whereby said motor can be driven at high rotational speeds together with the tool, and the motor can also function reliably without the need for intensive maintenance.
In accordance with the invention, this object is achieved in the case of a drive motor of the type described hereinabove in that it is a fluid-driven, gear-type motor incorporating interengaging gears which are sealed in a housing and have a rotational speed of between 40,000 and 150,000 revolutions per minute.
Surprisingly, it has been discovered that in contrast to fluid-driven turbine motors or rotary piston motors, fluid-driven gear-type motors are substantially better suited to employment in surgical apparatus. These motors are of very simple construction and merely comprise interengaging gears which are sealed on all sides in an encompassing housing together with a pressurised fluid supply conduit and a pressurised fluid outlet conduit, other moveable parts not being required, especially not radially displaceable disks such as are used in a rotary piston motor. This very simplified form of construction permits very high rotational speeds to be obtained and thereby the levels of performance to be attained such as are needed for employment in a surgical motor, for example, powers in the order of magnitude of 70 watts and upwards when using conventional pressures which may lie in a range of between 4 and 10 bar for example. There are scarcely any mutually rubbing parts in this new form of construction so that the necessity for lubrication is thereby reduced although the motor can nevertheless be driven at high rotational speeds without extensive maintenance being required.
The driving fluid may be a gas, for example, compressed air or nitrogen.
It is particularly advantageous for the gears of the gear-type motor to consist of a self-lubricating material, in particular, of polyoxymethylene (POM) or polyetheretherketone (PEEK). These self-lubricating materials permit operation to continue for particularly long periods of time and, moreover, it has been established that noise generation is relatively low when using such types of material so that the exhaust noises produced by the pressurised fluid emerging from the apparatus will remain within tolerable bounds.
It is advantageous for the outer diameter of the individual gears to be less than 40 mm. The diameter to width ratio of the gears may lie between 0.5 and 2.
The number of teeth on the gears should amount to at least 8. It is expedient if the modulus of the gears lies between 0.5 and 1.5.
This arrangement thereby results in a very compact constructional unit which requires very little space when employed in surgical apparatus and which, moreover, does not change the weight ratios of such an apparatus to a disadvantageous degree. This is of especial significance in the case of hand-held apparatus since the surgeon can then work for long periods of time with such types of hand-held apparatus without becoming unduly fatigued.
It is expedient if the bearing shaft of one of the gears of the gear-type motor is extended out from the housing of the gear-type motor in sealed manner and if it is coupled to a rotary tool without the intermediary of a reduction gear. The constructional outlay is also considerably reduced thereby, gear boxes can be completely dispensed with and the bearing shaft of the gear can be used directly as the drive shaft for the tool.
A particularly advantageous construction of a surgical apparatus is obtained when the housing of the gear-type motor is insertable into the tool holder of the surgical apparatus in a direction corresponding to that of the bearing shafts of the gears and is releasably fixed therein. The apparatus can then be easily dismantled, it sufficing to merely withdraw the motor out of the tool holder so that the tool holder can then be cleaned and sterilised in a conventional manner.